1. Field of the Invention (Technical Field)
The invention relates to a reactor apparatus, and method for its use, utilizing water or other fluid at supercritical temperature and pressure to accelerate the oxidation of fuels and/or the breakdown of substances, particularly hazardous substances.
2. Background Art
Mankind's need to develop more efficient uses of non-renewable energy sources is well-documented and nearly universally recognized. Considerable attention has been directed toward solving the dual problems posed by the widespread inefficient combustion of hydrocarbon fuels: the limited quantity of remaining proven petroleum reserves, and the environmental degradation attributed to hydrocarbon combustion. Concerns about the depletion of non-renewable energy sources, coupled with the anticipated energy demands of the coming decades, demand the development of energy-efficient uses of fossil fuels. Moreover, and with increasing frequency, inefficient combustion of fossil fuels is blamed for the "greenhouse effect" and other adverse atmospheric impacts, as well as deleterious impacts upon human health.
Similarly, the need safely to dispose of hazardous wastes, especially toxic and carcinogenic by-products of manufacturing and research processes, has commanded substantial public and governmental attention in the past two decades. The federal and state governments have responded to public pressure by adopting various statutes and regulations requiring that hazardous wastes be managed and disposed of properly with minimized risk to the public and the environment. Probably the most comprehensive and detailed plan for requiring safe management and disposal of hazardous waste is the federal Resource Conservation and Recovery Act of 1976 ("RCRA"), 42 U.S.C. .sctn..sctn.6901, et seq., as amended through 1990, and the regulations promulgated thereunder.
A vital portion of the federal RCRA regulations, comprising some 461 pages of material, are located at Title 40, Parts 260-270, of the Code of Federal Regulations, as amended through 1992. RCRA and its regulations include a detailed permitting process for managing hazardous wastes "from cradle to grave," and impose permitting and performance standards upon persons generating and transporting hazardous wastes, as well as facilities treating, storing, or disposing of hazardous waste. Performance and operating standards for frequently encountered methods and/or facilities for treating or disposing of hazardous waste (including incinerators) are found at Part 264 of Title 40 of the Code of Federal Regulations.
Despite continued efforts to accomplish safe hazardous waste disposal, a profound need remains for a means of disposing of hazardous waste that is completely thorough. Many existing modes of waste disposal (i.e. landfills, surface impoundments) simply move hazardous substances from one "high risk" biosphere to some other "low risk" biosphere perceived to be removed from potential exposure to humans. Many common disposal methods thus focus on isolating hazardous waste, rather than eliminating it. Alternatively, and with increasing frequency due to public pressure, hazardous waste is treated in an effort to eliminate or neutralize its hazardous characteristics. Treatments may be chemical or biochemical in nature, as in combustion or microbial biodegradation. Combustion, i.e. high-temperature incineration, once thought a preferred treatment of the future, is falling from public favor due to fears of incomplete combustion and resulting air pollution (especially NO.sub.x compounds) and high operational costs.
A promising solution to the above problems is posed by the burning of fuels and wastes using accelerated oxidation in specially devised reactors. Supercritical oxidation reactors use oxidizer mixtures, typically including water, at supercritical conditions to initiate a redox reaction with a fuel. The use of supercritical water in the oxidizer mix is desirable, as the supercritical state of the mix accelerates the reaction and boosts reaction efficiency, thus minimizing unreduced (and therefore still-harmful) exhaust.
In the typical example of the present art, the reaction takes place in an unlined cylindrical pressure vessel composed of high-grade steel or other expensive alloy capable of withstanding the temperature and corrosive effects of the reaction. The fuel and the supercritical oxidizer mix typically are externally heated and then introduced through a port at one end of the cylinder and immediately allowed to mix. The temperature of the fluids and the pressure within the vessel cause the resulting mix spontaneously to react. In the existing art, the reaction may be an uncontrolled detonation with reactor damage, due to the rich mixtures coming into rapid and complete contact within very short frames of time and space.
The reaction by-products typically are ejected from the opposite end of the pressure vessel, but not before substantial amounts of precipitates and scale have had an opportunity to accumulate upon the interior surfaces of the vessel. Existing reactors are frequently fouled with sufficient accumulates to impair reactor performance. Moreover, these reactor devices, being comprised of a simple single-walled chamber, are also inefficient sources of heat energy. Usually, the reaction is sustained by the addition of heat directly through the vessel walls; attempts to extract the heat of reaction through the same walls, therefore, is complicated at best.
U.S. Pat. No. 3,519,396 to Eagle, et al., entitled Means for Injecting a Gaseous Reactant, describes an apertured and chambered device for mixing gaseous reactants.
U.S. Pat. No. 3,852,192 to Fassell, et al., entitled Reactor for Wet Oxidation of Organic Matter, discloses a compartmentalized apparatus for performing wet oxidation of organic matter. Oxygen-containing gas is bubbled through an agitated aqueous medium to foster intimate association with the organic matter at reduced temperature.
U.S. Pat. No. 4,229,296 to Wheaton, et al., entitled Wet Oxidation System Employing Phase Separating Reactor, teaches a chambered device for accomplishing wet oxidation utilizing a gas phase/liquid phase separator feature.
U.S. Pat. No. 4,792,408 to Titmas, entitled Method and Apparatus for Enhancing Chemical Reactions at Supercritical Conditions, discloses a device for inducing chemical reactions at supercritical conditions; the very large apparatus does not incorporate any means for gradually or uniformly dispersing a reactant into the reaction chamber to enhance reactor performance.
U.S. Pat. No. 4,793,919 to McCorquodale entitled Wet Oxidation System, describes a system for accomplishing oxidation of organic matter in an aqueous medium under elevated temperatures and pressures.
U.S. Pat. No. 4,869,833 to Binning, et al., entitled Method and Apparatus for Controlled Chemical Reactions, teaches a system for effecting accelerated chemical reactions at elevated temperatures and pressures within a tubular reaction coil. Reactants may be introduced at various locations, but no permeable liners are disclosed.